Expanded beam lense inserts used in optical fiber connectors are currently made of an acrylic plastic rather than glass. A glass lense has many advantages over plastic lenses. Glass has an index of refraction closely matching that of optical fibers, resulting in lower reflection losses; it transmits in the wavelength range of 1.1-1.5 microns where plastic absorbs; it is more stable under extreme temperature conditions; durable antireflection coatings can be applied to glass; and the thermal expansion of glass is lower than that of plastic and matches that of the optical fiber, thereby maintaining the integrity of the fiber alignment.
A sol-gel process has been used to make monoliths of optical quality glass as related in U.S. Pat. No. 4,426,216 Satoh et al., Process for Producing Optical Glass; U.S. Pat. No. 4,323,381 Matsuyama et al., Method for Producing Mother preforms Rods for Optical Fibers; and Harmer et al., "The Sol-Gel Method for Optical Fiber Production", IFOC, Nov/Dec (1982) 40-44. However, the dimensional tolerances of the monoliths have not been maintained because of the shrinkage of the gel during drying and/or sintering. Quality glasses have also been made using colloidal techniques, but these glasses require a higher sintering temperature than those made by the process described by an instant invention. This is because colloid-derived glasses have larger pore and particle sizes and the higher temperature processing and conditions increase the difficulty of maintaining dimensional tolerances. Another disadvantage of the colloidal technique is that in the multicomponent glasses there are compositional heterogeneities on the scale of the colloid.